It is known that a significant amount of aerodynamic drag is created when a vehicle travels at velocities typical on a modern roadway. This is due, in large part, to areas of low pressure that are induced on rear surfaces of the vehicle. The low pressure becomes more pronounced as airflow over the vehicle separates from the vehicle surfaces. The phenomenon of airflow separation is also well known in aircraft wing design and, in this case, causes the wing to stall.
Vehicles having blunt rear ends are especially affected by airflow separation starting at an abrupt transition to a rear—near vertical surface. The low pressure that the airflow separation induces is compounded by a relatively large area on which the low air pressure acts in comparison with more streamlined vehicles.
The low air pressure acting on the rear surfaces of a moving vehicle produces a force that resists forward motion of the vehicle. This force is opposed by the vehicle's engine and requires power that is typically produced by burning fuel. Any reduction in aerodynamic drag results in a reduction in fuel consumption.
In a current era of high fuel prices and increasing environmental consciousness, fuel efficiency improvements are a growing concern. Aerodynamic improvements are especially valuable since they can be combined with other improvements such as engine efficiency and reduced chassis weight. Increasing fuel efficiency also provides the valuable benefit of increasing a vehicle's range of travel between refueling.
The present disclosure employs a technique of adding tapered rear surfaces to a vehicle. A similar streamlining principle is practiced with other vehicles such as high-speed cars and airplanes. It has also been applied to over-the-road trucks where the tapered rear surfaces are collectively known as a “boat-tail”.